Orbital parallax of binary systems compared to GAIA DR3 and the parallax zero-point offset at bright magnitudes

TL;DR

This study compares orbital parallax measurements of binary systems with Gaia DR3 parallaxes, assessing the zero-point offset at bright magnitudes and demonstrating the potential of orbital parallaxes for precise distance determination.

Contribution

It provides a comprehensive comparison between orbital and Gaia parallaxes, evaluates correction recipes for zero-point offset, and highlights the potential of orbital parallaxes with future Gaia data releases.

Findings

Orbital parallaxes agree with Gaia parallaxes within errors after corrections.

Only a subset of systems benefits from Gaia NSS analysis improvements.

Most orbital parallaxes reach better than 5% precision.

Abstract

(abridged)Multiple systems for which the astrometric and spectroscopic orbit are known offer the unique possibility of determining the distance to these systems directly without any assumptions. They are therefore ideal objects for a comparison of Gaia data release 3 (GDR3) parallax data, especially since GDR3 presents the results of the non-single star (NSS) analysis that potentially results in improved parallaxes. An sample of 192 orbital parallax determinations for 186 systems is compiled from the literature. The stars are also potentially in wide binary systems, and 37 candidates were found. Only for 21 objects does the NSS analysis provide information, including 8 from the astrometric binary pipeline, for which the parallaxes do improve significantly compared to those in the main catalogue. It appears that most of the objects in the sample are eliminated in the pre-filtering stage of the NSS analysis. The difference between the orbital parallax and the (best) \G\ parallax was finally obtained for 170 objects. When objects with large parallax errors or unrealistically large differences between the orbital and \G\ parallaxes are eliminated, and objects with a GOF < 100 or <8 are selected, samples of 68 and 20 stars remain. Three recipes that calculate the PZPO are tested. After these corrections are applied the remaining parallax differences are formally consistent with zero within the error bar for all three recipes. The method of using orbital parallaxes is shown to work, but the full potential is not reached as an improved parallax from the NSS analysis is available for only few systems. In the final selection, the orbital parallax of 18 of 20 stars is known to better than 5%. In the full sample, 148 objects reach this precision and therefore the full potential of using orbital parallaxes may hopefully be reached with GDR4.